[论文解读] Effect of homogenization on precipitation behavior and strengthening of 17-4PH stainless steel fabricated using laser powder bed fusion

Kun Li, Soumya Sridar+2 more|arXiv (Cornell University)|Dec 12, 2021

Additive Manufacturing Materials and Processes被引用 5

一句话总结

本研究 investigates post-heat treatment via homogenization at 1050 °C for varying durations followed by aging at 482 °C for 1 hour to optimize precipitation behavior and mechanical properties in laser powder bed fusion-fabricated 17-4PH stainless steel. Homogenization for 1 hour refined martensite and prior austenite grains, dissolved incoherent ε-Cu precipitates, and enabled re-precipitation of coherent Cu-rich clusters, resulting in superior tensile strength and ductility exceeding traditionally processed 17-4PH steels.

ABSTRACT

Effective post-heat treatment is critical to achieve desired microstructure for high-performance in additively manufactured (AM) components. In this work, the influence of homogenization on microstructure-property relationship in 17-4PH steels has been investigated. Precipitation of NbC, oxides, and ε-Cu were observed in the as-built 17-4PH steels. To design an optimum post-heat treatment, homogenization was performed at 1050oC for different times followed by aging at 482oC for 1 hour. It was identified that homogenization for 1 hour followed by aging leads to the best combination of strength and ductility due to the refinement of martensite and prior austenite grains. Improved tensile properties were achieved for the post-heat-treated alloys that exceeded the traditionally fabricated 17-4PH steels. Through comprehensive microstructure characterization, it was deduced that the incoherent ε-Cu precipitates in the as-built alloy were dissolved through homogenization, and subsequently, re-precipitated as coherent Cu-rich clusters during aging. This study demonstrates that altering the precipitation behavior using post-heat treatment is an effective pathway to significantly improve the mechanical properties of AM alloys.

研究动机与目标

• To understand the influence of homogenization on precipitation behavior in additively manufactured 17-4PH stainless steel.
• To identify optimal post-heat treatment parameters that enhance microstructure refinement and mechanical performance.
• To improve tensile properties beyond those of conventionally processed 17-4PH steels through controlled heat treatment.

提出的方法

• Laser powder bed fusion (LPBF) was used to fabricate 17-4PH stainless steel components.
• Homogenization was performed at 1050 °C for 0.5, 1, 2, and 4 hours to dissolve incoherent precipitates.
• Subsequent aging was conducted at 482 °C for 1 hour to promote re-precipitation of strengthening phases.
• Microstructure was characterized using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS).
• Tensile testing was performed to evaluate mechanical properties, including yield strength and elongation.
• Precipitation behavior was analyzed by tracking the evolution of NbC, oxides, and ε-Cu phases across heat treatment conditions.

实验结果

研究问题

• RQ1 How does homogenization duration at 1050 °C affect the microstructural evolution in LPBF-fabricated 17-4PH steel?
• RQ2 What is the role of homogenization in dissolving incoherent ε-Cu precipitates and enabling the formation of coherent Cu-rich clusters during aging?
• RQ3 How does grain refinement of martensite and prior austenite influence the tensile properties of post-heat-treated 17-4PH steel?
• RQ4 Can post-heat treatment via homogenization and aging surpass the mechanical performance of traditionally processed 17-4PH steels?
• RQ5 What is the relationship between precipitation behavior and the resulting strength-ductility balance in additively manufactured 17-4PH?

主要发现

• Homogenization for 1 hour at 1050 °C followed by aging at 482 °C for 1 hour yielded the optimal balance of strength and ductility.
• The refined martensite and prior austenite grain structures were directly linked to improved tensile properties.
• Incoherent ε-Cu precipitates present in the as-built condition were completely dissolved during 1-hour homogenization.
• Coherent Cu-rich clusters re-precipitated during aging, contributing significantly to strengthening.
• Tensile strength and elongation of the post-heat-treated LPBF 17-4PH exceeded those of conventionally processed 17-4PH steels.
• Comprehensive microstructural analysis confirmed that homogenization enables a transition from incoherent to coherent precipitation, enhancing mechanical performance.